1. Field of the Invention
The present invention relates to a wire-cut electric discharge machine having a water level abnormality detection function and to a water level abnormality alarm generation cause specifying method.
2. Description of the Related Art
There are two types of wire-cut electric discharge machines. One is of a spraying type in which a machining tank is not filled with a machining liquid but machining is performed while spraying a machining liquid onto a wire electrode through nozzles fixed at an inlet and an outlet of each of upper and lower wire guides. The other is of a soaking type in which a workpiece is secured inside of a machining tank in order to enhance a machining speed and a machining accuracy, the machining tank is filled with a machining liquid, and then, the workpiece is soaked in the machining liquid.
In a wire-cut electric discharge machine of the soaking type, the water level of the machining tank need to be varied according to the height of the workpiece, and therefore, various water level adjusting mechanisms are devised, as the following items 1) to 3).
1) A type in which the water level is adjusted to the height of the workpiece by manually moving an overflow gate in a vertical direction;
2) another type in which the overflow gate is driven by an actuator in such a manner as to automatically follow a height of a Z axis for holding an upper wire electrode therein (generally, the height of the Z axis and the height of the workpiece establish a proportional relationship); and
3) a further type provided with a water level detecting unit such as a pressure gage capable of sequentially detecting a water level and a water level adjusting mechanism for feeding back a signal from the water level detecting unit so as to adjust the water level. The water level adjusting mechanism of this type can be used in a situation in which the water level need to be set irrespective of the height of the Z axis for holding the wire electrode therein (e.g., a situation in which water is drained only to a level of a workpiece mount during automatic wire connection in order to minimize a change in temperature when the workpiece is replaced with another).
Japanese Patent Application Laid-open No. 4-300123 discloses a technique of a wire-cut electric discharge machine provided with a water level automatic adjusting technique for automatically replenishing a machining liquid which is decreased in quantity during operation of the machine.
Although not in the technical field of the wire-cut electric discharge machine, Japanese Patent Application Laid-open No. 1-81008 discloses a technique of providing a knowledge base section, in which expert knowledge about a diagnosis of a cause of failure is accumulated, inputting the expert knowledge into the knowledge base section via interaction unit, and eliciting the cause of the failure in accordance with the knowledge base section.
Otherwise, Japanese Patent Application Laid-open No. 3-154847 discloses a technique of diagnosing a cause of failure in accordance with a failure tree (i.e., a failure result estimation tree diagram) having a configuration in which a plurality of alternatives are provided with respect to one question relating to a cause of failure diagnosing object, and, from each of these alternatives, some questions and alternatives are branched, and then an alternative in a final stage reaches the cause of the failure, respectively.
The workpiece or a table mounting the workpiece thereon is deformed due to thermal expansion caused by a change in temperature, thereby causing degradation of machining accuracy or disconnection of the wire electrode. As a consequence, the change in temperature needs to be suppressed to the minimum in order to achieve machining with high accuracy in the wire-cut electric discharge machine. In view of this, the water needs to be stored in the machining tank even during an initial setup.
Therefore, it is desirable to use the above-described electric discharge machine of the soaking type provided with the water level detecting unit for sequentially detecting the water level and the water level adjusting mechanism for feeding back the detection signal so as to adjust the water level.
However, the water level detecting unit or the water level adjusting mechanism is exposed to sewage including sludge (metallic fine powder) produced by an electric discharge machining. As a consequence, there arises a problem that a failure caused by fixture of the sludge or abrasion due to the sludge is liable to occur in the water level detecting unit or the water level adjusting mechanism. Actually, in case where a failure occurs in a water level adjusting system including the water level detecting unit and the water level adjusting mechanism, it is necessary to suppress a down time (i.e., an inoperable time) of the electric discharge machine to a short period of time.